After surgery, women diagnosed with hormone-receptor-positive breast cancer usually take hormonal therapy medicine to reduce the risk of the cancer coming back (recurrence). Hormonal therapy medicines work in two ways:

by lowering the amount of estrogen in the body

by blocking the action of estrogen on breast cancer cells

There are several types of hormonal therapy medicines. Tamoxifen, a selective estrogen receptor modulator (SERM), is one of the most well-known. Tamoxifen can be used to treat both premenopausal and postmenopausal women. In early 2000, the aromatase inhibitors:

Arimidex (chemical name: anastrozole)

Aromasin (chemical name: exemestane)

Femara (chemical name: letrozole)

were shown to be more effective at reducing recurrence risk in postmenopausal women and are now used more often than tamoxifen to treat women who’ve gone through menopause.

Aromatase inhibitors aren’t commonly used to reduce recurrence risk in premenopausal women. Still, in some cases a premenopausal woman may take medicine to suppress the function of her ovaries and take an aromatase inhibitor.

In most cases, tamoxifen and the aromatase inhibitors are taken for 5 to 10 years.

Both tamoxifen and aromatase inhibitors can cause side effects. Tamoxifen may cause hot flashes and increase the risk of blood clots and stroke. Aromatase inhibitors may cause muscle and joint aches and pains.

Both tamoxifen and the aromatase inhibitors also may cause vaginal dryness and lower your sex drive, which doctors call loss of libido.

When estrogen levels drop, the membranes of the vagina get thinner, become less flexible, and produce less lubricating fluid. Sexual intercourse may be uncomfortable or even painful. Vaginal dryness, the stress of a breast cancer diagnosis and treatment, as well as other side effects can make sex the last thing you want to think about. While these side effects aren’t life-threatening, they can lead to a much worse quality of life for many women.

Low-dose vaginal estrogen and testosterone creams and Estring (a plastic ring filled with estrogen that is inserted into the vagina) have been used to help ease vaginal dryness and sexual dysfunction. Still, because these treatments put hormones into the vagina, doctors have worried that they may increase the risk of recurrence in women who’ve been diagnosed with hormone-receptor-positive breast cancer.

A small study suggests that Estring and vaginal testosterone cream seem safe and effective for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer who are taking an aromatase inhibitor and experiencing vaginal dryness and/or loss of libido.

To figure out if the testosterone cream and Estring were safe for women who had been diagnosed with breast cancer, the researchers looked to see if the cream or Estring caused a woman’s estradiol levels to go up and stay up. Estradiol is a form of estrogen. If estradiol levels went up and stayed up, this would likely affect the risk of recurrence because hormone-receptor-positive breast cancers are signaled by estrogen to grow.

The study included 69 postmenopausal women who had been diagnosed with early-stage, hormone-receptor-positive breast cancer and were taking an aromatase inhibitor. The women ranged in age from 37 to 78 years old. All the women reported that they were having vaginal dryness or loss of libido.

The researchers randomly assigned the women to one of two treatments for 12 weeks:

testosterone cream that was applied inside the vagina (34 women)

Estring, a plastic ring filled with estrogen that is inserted into the vagina (35 women)

The researchers measured each woman’s estradiol levels three times: at the beginning of the study before either treatment started, 4 weeks after the study started, and at 12 weeks after the last treatment.

The women also had a gynecologic exam and filled out a sexual quality-of-life questionnaire at the beginning of the study and at the end of the study.

The researchers defined elevated estradiol levels as greater than 10 picogram/milliliter (pg/mL) and at least 10 pg/mL above the estradiol level at the beginning of the study after starting treatment on two consecutive tests at least 2 weeks apart.

If more than 25% of the women had elevated estradiol levels for a long time, the treatment that caused the elevated levels would be considered unsafe.

The researchers found that none of the women who used the Estring had long-term elevated estradiol levels, and 3 of the 34 (12%) women using the testosterone cream had long-term elevated estradiol levels.

Interestingly, 37% of the women in the study had elevated estradiol levels at the beginning of the study. The researchers said this could be because the women were taking supplements that contained estrogen.

All the women in the study said the treatments eased vaginal dryness and boosted their sex drive.

Based on the results, the researchers concluded that both the testosterone cream and the Estring were safe and effective for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer who were having vaginal dryness and loss of libido side effects from taking an aromatase inhibitor.

While the results sound promising, there are some things to keep in mind about the study:

It was a small study. Only 69 women participated. A larger study would offer more widely applicable results.

A high percentage of women had elevated estradiol levels when the study started.

How safe is safe enough? The American Menopausal Society and the American College of Obstetricians and Gynecologists recommend that women with a history of hormone-receptor-positive cancer first try nonhormonal options, including vaginal moisturizers, pH balanced gels, topical oils, and lubricants for vaginal atrophy. The groups recommend that treatments that use hormones be reserved for women who aren’t helped by these nonhormonal options and only after consultation with their medical oncologists.

If you’re experiencing vaginal dryness or a low sex drive because of breast cancer treatment, it’s a good idea to talk to your doctor about nonhormonal treatment options first. It’s also a good idea to talk to your partner about how you’re feeling.

If nonhormonal options aren’t working, then talk to your doctor about Estring or low-dose estrogen or testosterone cream. Together, you and your doctor can talk about the risks and benefits and decide if this might be right for your unique situation.